Introduction to Earth

1. INTRODUCTION TO
EARTH

2. SOME FACTS ABOUT THE EARTH
Earth is the only planet to be named in English. The
word ‘Earth’ is Old English word for "land“
Earth belongs to the Milky Way Galaxy, Local Group
Cluster and Virgo Super Cluster
Earth is the only planet to sustain life
Earth is believed to be existent for 450 million years
& evidences are from 225 million years

3. SOME FACTS ABOUT THE EARTH

4. SOME FACTS ABOUT THE EARTH
Earth is the third planet from the sun
Earth is the fifth largest planet in the universe
The distance of the earth from the sun is 149,600,000 km
The diameter of the sun is 100 times the diameter of the
earth
The mass of the earth is 5.972 x 10
24
kg
The Surface area of earth is 510,072,000 km²

5. SOME FACTS ABOUT THE EARTH
Before 500 BC, people thought that earth was flat. But
thanks to scientists like Aristotle and Pythagoras, people
know that the shape of the earth is spherical. However Sir
Isaac Newton showed that the earth was not a perfect
sphere, but a compressed spheroid.
The correct technical term to use will be oblate spheroid, a
type of ellipsoid solid formed when an ellipse is rotated
about its minor axis.
The study of size and shape of earth is called geodesy.
The diameter of earth at poles is 12715 km (minor axis)
The diameter of earth at equator is 12763 km (major axis)

6. STRUCTURE OF EARTH
The structure of earth (also
referred as cross–section) is
divided into mainly four layers
namely Crust, Mantle, Inner
Core and Outer Core.

7. STRUCTURE OF EARTH

8. STRUCTURE OF EARTH
Divisions,Thickness & Materials of the layer

9. STRUCTURE OF EARTH
The outermost layer of the Earth is the crust. It is also the surface of the
earth.

This comprises the continents and ocean basins and therefore it has been
classified into continental crust and oceanic crust.
The oceanic crust extends up to a distance of 0-10 kms (5-12 taken as
average) whereas the continental crust would extend up to 0-75 kms (20-70
taken as average).
The oceanic crust is mainly composed of basaltic igneous rocks, mainly of
silica and magnesium and therefore also called SIMA layer.
The continental crust is composed of crystalline and granitic rocks mainly of
silica and aluminum and therefore also called SIAL layer.
CRUST

10. STRUCTURE OF EARTH
The next layer is the mantle, which is composed mainly of iron and
magnesium silicates. It is been referred as FeMa layer.
Mantle is also where most of the internal heat of the Earth is located. It is
about 2900 km thick.
It can be subdivided into four layers namely
(1) Lithosphere (70 – 100 kms)
(2) Asthenosphere (100 - 350 kms)
(3) Upper Mantle (350 – 670 kms)
(4) Lower Mantle (670 – 2900 kms)
Mohorovičić discontinuity, usually referred to as the Moho is the transition
boundary between the Earth's crust and the mantle.
MANTLE

11. STRUCTURE OF EARTH
The lithosphere is the outermost part of the mantle immediately below the
Mohorovičić discontinuity. It has a part of the tectonic plates that cover
surface of Earth.
Asthenosphere is a low seismic velocity zone where rocks are at or near
melting point. It also has a part of tectonic plates.
The lower mantle is probably mostly silicon, magnesium and oxygen
with some iron, calcium and aluminum.
The upper mantle is made up of mostly olivine and pyroxene
(iron/magnesium silicates), calcium and aluminum
MANTLE

12. STRUCTURE OF EARTH
The third layer is outer core. The outer core is a hot and liquid layer
comprising mainly of Nickel and (liquid) Iron. Therefore it is referred as NiFe
Layer.
The outer core may also contain lighter elements such as Si, S, C, or O.
The outer core ranges from 2900 kms to 5150 kms and is 2300 km thick.
The Earth's magnetic field is believed to be controlled by the liquid outer
core. It is also believed to be the responsible force of earth’s rotation and
electric currents.
The transition space between outer core and mantle is called Gutenberg
discontinuity
OUTER CORE

13. STRUCTURE OF EARTH
The fourth layer is inner core.
This layer stretches from 5150km to 6370 km and is nearly 1200 km
thick.
The inner core is mostly made of solid iron and has little amounts of
nickel.
It is unattached to the mantle and is suspended in the molten outer core.
The inner core is believed to have the extreme temperature and pressure
conditions.
The transition region between outer core and inner core is called Lehmann
discontinuity
INNER CORE

14. STRUCTURE OF EARTH

15. STRUCTURE OF EARTH

16. COMPOSITION OF EARTH
S.No.Component Percentage
by Mass
1 Iron 34.6%
2 Oxygen 29.5%
3 Silicon 15.2%
4 Magnesium 12.7%
5 Sulfur 2.4%
6 Nickel 1.9%
7 Calcium 1.5%
8 Aluminium 1.4%
9 Trace Elements0.8%
As discussed earlier, the mass of the Earth is approximately 5.98×10
24
kg.
When taken as a whole, the Earth's chemical composition (by mass) has been approximated
as given in the table below. The students should remember the top three with their percentages